This invention relates to zinc sulfide-based electroluminescent phosphors and more particularly to a method and apparatus for coating such phosphors with a moisture inhibiting coating.
Still more particularly, it relates to a method and apparatus for making such phosphors in commercial quantities.
It is known from U.S. Pat. No. 6,064,150 that a coating of aluminum nitride or aluminum nitride amine on an electroluminescent phosphor particle allows the manufacture of electroluminescent light sources having good life characteristics. It is also known to coat such phosphors with a metal oxide hydroxide.
It would be an advance in the art if such coatings could be applied to large batches of phosphor materials.
It is, therefore, an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance the manufacture of commercial quantities of coated electroluminescent phosphors.
These objects are accomplished, in one aspect of the invention, by a process for preparing particles of zinc sulfide-based electroluminescent phosphor having a moisture resistant coating thereon which comprises the steps of selecting a reaction vessel having a given height and a porous disc at the bottom thereof; charging the reaction vessel with phosphor particles and fluidizing the particles by introducing an inert gas into the vessel through the porous disc; heating the reaction vessel to a reaction temperature; introducing a coating precursor into the reaction vessel at a position adjacent the bottom of the vessel but above the disc; introducing a co-reactant into the reaction vessel at a position substantially mid-way of the given height; and maintaining the inert gas flow, the precursor flow and the co-reactant flow for a time sufficient for a reaction to occur and coat the phosphor with the moisture resistant coating.
The apparatus for manufacturing commercial quantities of zinc sulfide-based electroluminescent phosphor having a moisture resistant coating thereon, comprises a reaction vessel having a given height and a porous disc at the bottom thereof; a supply of phosphor particles within the vessel; a first supply of an inert gas for fluidizing the particles, the first supply of inert gas entering the vessel through the porous disc; a heater surrounding the reaction vessel for heating the reaction vessel to a reaction temperature; a supply of a coating precursor; first means for conducting the coating precursor from the supply to the reaction vessel, the first means entering the reaction vessel at the bottom of the vessel at a position above the porous disc; a supply of a co-reactant; and a second means for conducting the co-reactant from the supply to the reaction vessel, the second means entering the reaction vessel at a position substantially mid-way of the given height.
This method and apparatus allows for the commercial production of sizeable quantities of coated electroluminescent phosphor.